Heavy Constant Rain
When we grow bonsai we always hope that we do not have to face or deal with extremes in weather.
Sometimes heavy constant rain can be a problem. Usually the results I see are that the bonsai seems to grow with a greater vigour than before. But this is not always the case.
If the root ball is so saturated that it doesn’t allow the water to drain away, then the potential for the roots to rot is rather high. The roots are resting in water logged soil. You will not really know this is happening until the leaves begin to change colour and fall off, and the bonsai is effectively dead.
The best way that I know to stop this from happening is to provide adequate drainage.
The Pot
· Make sure that the pot has good sized holes in the base to allow the water to exit as quickly as possible.
o Cover the hole with material that is going to stop the soil from washing through it.
· Some bonsai enthusiasts have a layer of pea metal covering the base to allow the water to drain to the holes.
o I’ve never been too sure how this actually works in the shallow pots that we use.
o In deep pots where the soil is placed towards the top, I can understand that an area underneath filled with pea metal will be good for drainage.
· The pot needs a space underneath of 5 mm to 10 mm above the shelf.
o This stops the water from ponding under the pot by capillary attraction.
o It allows the water to drain away and for air to pass through the gap to keep it dry.
The Soil
· If you experience heavy constant rain for a very long time, remember that you may have to provide some liquid fertilizer to replace those nutrients that have been washed out.
· The soil mix that you use needs to be ‘free draining’.
o This means that the fine soil particles have been removed.
o There are many benefits that your bonsai will enjoy from this one action.
o If you do not have the bonsai set of sieves then use your kitchen flour sieve or its equivalent.
o If you can, include about ⅓ pea metal in your soil mix. The pea metal acts to keep the soil more open and friable.
o It allows the roots to penetrate the soil easier and the subsequent growth is more robust. It also allows the replacement of stale air with oxygen rich air.
o Oxygen is required by the roots to grow. The fine soil particles dictate how fast the water passes through the soil.
o If on a normal watering day it takes more than 5 seconds for the water to disappear from the surface, then the soil is clogged up with fine particles. The amount of moss growing on the top can be better controlled.
o If the moss is too thick it will stop the water from getting into the root ball. The weeds in a friable mix are easily removed.
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Ground Cover
· My mix is friable and has the majority of fine particles removed.
· I also keep the soil level 10 mm to 15 mm below the top edge of the pot.
o This space is filled with pea metal. (Pea metal is a stone chip of approximately 5 mm diameter.) It reduces the speed of evaporation and maintains the moisture within the root ball.
Check after heavy constant rain that the water has evaporated from around the bonsai. If it is still wet underneath, then it is more than possible that the root ball is water logged and the bonsai is in danger of suffering root rot.
Be happy and use a friable mix,
Bonsaibevan.
